JP3660802B2 - Metal tube thickening processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for increasing the thickness of a metal tube that forms a thick portion by increasing the thickness of a desired section in the longitudinal direction of a metal tube such as a square steel tube or a round steel tube.
[0002]
[Prior art]
Conventionally, a small area in the longitudinal direction of a metal pipe such as a steel pipe is locally heated by an induction coil or the like to form a red-heated heating section, and the heating section is moved while moving the heating section in the longitudinal direction of the metal pipe. By applying a compressive force in the longitudinal direction of the metal tube to increase the thickness sequentially, and cooling and solidifying the rear end portion of the heating part immediately after the thickness increase, so that no further increase in thickness occurs. A method for increasing the thickness of a metal tube is known in which the metal tube is continuously increased in thickness to a desired thickness. However, in this thickening method, the portion where the thickening is generated is not restrained at all, and unstable distortion may occur. For this reason, the thickening processing conditions (temperature, pressure, etc.) are strictly controlled. There was a need. Moreover, although the thick part formed by the thickening process may be heat-treated, an undesired deformation may occur when heated by the heat treatment.
[0003]
In order to solve these problems, the present applicants have previously inserted in advance a die having a length equal to or greater than the length of the thick portion to be formed in the region of the metal pipe to be thickened. In this state, the metal pipe was subjected to a thickening process, and a method of applying a heat treatment as needed was developed and a patent application was filed (see Japanese Patent Application Laid-Open No. 9-76011). This method can regulate the inner surface of the metal pipe where the thickening deformation occurs on the outer surface of the die during the thickening process, and can suppress unstable deformation during the thickening process. It also has the effect that the undesired deformation of the thick part can be suppressed on the outer surface of the die.
[0004]
[Problems to be solved by the invention]
However, if the inner surface of the thick part of the metal tube is regulated with a die during the thickening process, the inner surface of the thick part will be strongly pressed against the die, and the thick part will cool down when the thickening process or heat treatment is finished. It will be in the state tightened more strongly by contraction of. For this reason, not only a very large force is required when the die is pulled out from the metal tube, but the inner surface of the metal tube may be damaged when the die is pulled out. In some cases, it could not be pulled out.
[0005]
To solve this problem, it is conceivable to apply a lubricant to the surface of the die to improve the slip, but since the temperature becomes extremely high during the thickening process, the lubricant burns and the original performance Does not demonstrate. In view of this, Japanese Patent Application Laid-Open No. 9-76011 proposes a structure in which the dice can be enlarged or reduced or disassembled, and when the dice are pulled out, the diameter of the dice is reduced or disassembled and pulled out.
[0006]
However, dice that can be expanded and contracted and that can be disassembled are complicated in structure and expensive, and the structure is complicated, so that it is necessary to frequently perform maintenance, resulting in a high maintenance cost. In addition, the structural members are small and weak due to dimensional constraints. Therefore, the lifetime is also short, and these defects are more noticeable with smaller diameter tubes. In the case of a structure that can further expand and contract, it is necessary to have a structure in which the die is divided into a plurality of segments in the circumferential direction, so that the gap between the segments is large when the diameter is expanded to restrict the inner surface of the thick part. Therefore, the inner surface of the thick portion cannot be satisfactorily regulated at the gap portion, and the shape of the thick portion may be deteriorated. This drawback is particularly noticeable in the case of circular tubes. Moreover, when it was set as the structure which can be decomposed | disassembled, at the time of die drawing | extracting, it was necessary to decompose | disassemble, and there also existed a problem that workability | operativity was bad.
[0007]
The present invention has been made in view of such problems, and in a method of increasing the thickness by a method of restricting the inner surface of a metal tube with a die, the die can be easily formed without using a dice having a structure that can be expanded and contracted. An object of the present invention is to provide a method for increasing the thickness of a metal tube that can be pulled out.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention uses a die having a gradient in which the drawing side from the metal tube has a large diameter along the longitudinal direction of the metal tube on the outer surface as the die inserted into the metal tube. Is. If the dies are provided with a gradient in this way, when the dies are pulled out of the metal tube, the dies are placed in the longitudinal direction of the metal tube and large in size even if the inner surface of the metal tube is strongly pressed against the outer surface of the die. The contact pressure between the die and the metal tube is rapidly reduced only by moving it slightly to the radial side, and the force required for drawing becomes extremely small and stable. For this reason, without performing operations such as reducing the diameter of the die when it is pulled out or disassembling it, the die can be easily pulled out and the inner surface of the metal tube is not damaged.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the present invention has a length equal to or greater than the length of the thick part so as to be positioned inside the thick part formed by the thickening process in the metal tube to be thickened. A die is inserted in advance, and in this state, a small region in the longitudinal direction of the metal tube is locally heated by a heating device to form a red-hot heating portion, and the heating portion is moved in the longitudinal direction of the metal tube. The metal tube is continuously increased in thickness by applying a compressive force in the longitudinal direction of the metal tube to the heating portion while gradually increasing the thickness, and cooling the rear end portion of the heating portion immediately after the thickness increase. In the method of forming a thick portion on the outside of the die, a configuration is used in which the die is a die that has a gradient with a large diameter on the extraction side from the metal tube along the longitudinal direction of the outer surface of the metal tube. It is what. In this configuration, the thickening of the metal tube is performed outside the die placed at a fixed position. Therefore, unfavorable deformation that tends to occur during thickening can be regulated on the outer surface of the die, and the thickening can be stably and satisfactorily performed. Can be performed. And after finishing the thickening process, the thick part is pressed against the outer surface of the die, but when drawing the die, it is in the direction toward the large diameter side of the die and the length of the metal tube If the directional force or impact is applied, the gap between the die and the metal tube is created due to the gradient of the outer surface of the die, and the contact pressure is rapidly reduced. The die can be easily pulled out without damaging the surface.
[0010]
Here, a configuration in which the thickening portion of the thick portion when the thickening process is performed in a state where the sloped die is inserted into the metal tube is constant in the longitudinal direction of the metal tube and the thick portion having a constant thickness is formed. However, with this configuration, a gradient that follows the gradient of the die is formed on the outer surface of the thick portion, and the outer diameter may change in the longitudinal direction. Therefore, if the dimensional tolerance of the outer surface of the thick wall portion is strictly required, it is necessary to eliminate the gradient of the outer surface of the thick wall portion. By adopting a configuration in which the thickness is increased while adjusting according to the direction position and the gradient of the die, the outer diameter of the thick portion can be made constant along the longitudinal direction of the metal tube.
[0011]
The gradient formed on the above-described die is preferably large from the viewpoint of easily removing the die, but is preferably as small as possible from the shape of the thick portion formed by thickening. As a result of confirmation by the present inventors, it was possible to easily remove the dice even when the dice gradient was set to about 1/1000. Therefore, the dice gradient is preferably set to about 1 / 1,000 to 1/100.
[0012]
In another embodiment of the present invention, a small region in the longitudinal direction of the metal tube to be thickened is locally heated by a heating device to form a red-hot state heating portion, and the heating portion is formed in the longitudinal direction of the metal tube. The metal tube is continuously moved by applying a compressive force in the longitudinal direction of the metal tube to the heating portion while moving in the direction to increase the thickness sequentially, and cooling the rear end portion of the heating portion immediately after the thickness increase. In the method of forming a thick part by increasing the thickness, a die having a gradient along the longitudinal direction of the metal tube is pulled out on the outer surface so that it is located inside the heating part of the metal tube, and the large diameter side of the gradient is pulled out. which has a configuration in which the Rutotomoni the die is positioned so that and becomes a lateral moving direction side with respect to the metal tube of the heating portion is tuned to move with respect to the metal tube of the heating unit is moved relative to the metal tube It is. Even in this configuration, during the thickening process, there is a die on the inner surface of the portion of the metal tube where the thickening deformation occurs, and undesirable deformation of the inner surface is suppressed, and a good thickening process can be performed. In addition, when the die is pulled out, it can be pulled out easily and without damaging the inner surface of the metal tube due to the gradient of the outer surface. In this case, since the die supports only a part of one end of the thick portion formed by thickening, it is not necessary to make the gradient provided in the die so small, for example, 1/10 to 1 / It is preferable to be about 2.
[0013]
【Example】
Hereinafter, preferred embodiments of the present invention shown in the drawings will be described.
1 is a schematic cross-sectional view showing a preferred example of a thickening apparatus used for carrying out the method of the present invention, FIGS. 2 (a) and 2 (b) are cross-sectional views taken along arrows AA and BB in FIG. 1, respectively. FIG. 3 is a schematic sectional view showing a thick portion and a die at the end of the thickening process. Reference numeral 1 denotes a metal pipe to be thickened, and a square steel pipe is used in this embodiment. As can be seen from FIG. 2, the metal tube 1 includes four flat tube walls (hereinafter referred to as side walls) 1a and four corner-shaped arcuate tube walls (hereinafter referred to as corner walls) 1b. Reference numeral 2 denotes a fixed support for fixing and holding one end of the metal tube 1 at a fixed position, and 3 denotes a movable support that holds the opposite end of the metal tube 1 and is movable in the axial direction of the metal tube 1. The movable support 3 is connected to a compression device (not shown) such as a hydraulic cylinder, so that a compressive force can be applied to the metal tube 1 via the movable support 3.
[0014]
Reference numeral 4 denotes a heating device that can locally heat a small region in the longitudinal direction of the metal tube 1 to form a red-hot state heating unit 5. Here, an induction coil is used. Reference numeral 6 denotes a cooling device attached to the heating device 4. When the heating device 4 moves in the direction indicated by the arrow C, a cooling medium 7 such as cooling water is sprayed on the rear side of the heating unit 5. A moving device 8 moves the heating device 4 and the cooling device 6 along the metal tube 1 at a desired speed. The moving table 8a moves while holding the heating device 4 and the cooling device 6, and the moving table 8a. And a servo motor 8c for rotationally driving the feed screw 8b. The moving device 8 is not limited to the one shown in the illustrated embodiment, and can be appropriately changed such as a device using a motor and a feed chain and a device using a hydraulic cylinder.
[0015]
Reference numeral 10 denotes a die arranged inside the metal tube 1 for suppressing unstable deformation that may occur when the metal tube 1 is thickened. In this embodiment, as shown in FIG. 2, a square tube having an outer surface similar to the inner surface of the metal tube 1 is used as the die 10, and a flat side wall die surface 10 a facing the flat side wall 1 a of the metal tube 1. And an arc-shaped corner die surface 10b facing the arc-shaped corner surface 1b of the metal tube 1. The die 10 is held on a support shaft 12 via a support member 11 disposed at an appropriate interval in the longitudinal direction on the inside thereof, and the support shaft 12 extends toward the movable support 3 side, and the die 10 Is connected to a die moving device (not shown) such as a hydraulic cylinder for taking in and out the metal pipe 1.
[0016]
The length of the die 10 is made longer than the length L of the thick portion 1A formed in the metal tube 1. Furthermore, the outer surface of the die 10 is provided with a gradient along the longitudinal direction of the metal tube 1 over its entire length. As shown exaggeratedly in FIG. 3, this gradient is such that the drawing side of the die 10 from the metal tube 1 (left side in FIGS. 1 and 3) has a large diameter, that is, the outside diameter D ₁ on the drawing side. Is larger than the outer diameter D ₂ on the opposite side. In the present specification, the term “diameter” is not limited to the diameter of a circular cross section, but also indicates the diameter (dimension on a straight line passing through the center) of a square cross section as shown in FIG. The diameters D ₁ and D ₂ are distances between the pair of side wall die surfaces 10a. The magnitude of the gradient is usually set to about 1/1000 to 1/100 (inclination angle θ is 0.057 ° to 0.57 °).
[0017]
The outer diameter of the die 10 is determined so that a gap is formed between the die 10 and the metal tube 1 so that the die 10 can be easily inserted into the metal tube 1. Further, the gap g (see FIG. 2) between the die 10 and the metal tube 1 causes undesirable deformation (for example, deformation in which the flat side wall 1a of the metal tube 1 is recessed inward) that may occur during the thickening process. It is determined so that it can be suppressed by the die 10. More specifically, the gap g (see FIG. 2) between the die 10 and the metal tube 1 is based on the amount of displacement to the inside of the inner surface of the metal tube 1 due to the thickening (usually 1/2 of the thickening amount). May be determined so that the inner surface of the thick portion 1A which is thickened during the thickening process of the metal tube 1 can always be regulated by the outer surface of the die 10, or to the inner surface of the metal tube 1 When the metal tube 1 is thickened in a normal shape, the inner surface of the thick portion hardly comes into contact with the outer surface of the die 10, but an undesirable deformation such that the flat side wall 1a is recessed inward. It may be determined so that the inner surface can be regulated when it occurs.
[0018]
Next, a thickening operation using the thickening apparatus having the above configuration will be described. In FIG. 1, a metal tube 1 to be thickened is held at a predetermined position by a fixed support 2 and a movable support 3, and a die 10 is inserted into a region where the thick portion 1A of the metal tube 1 is formed, Stop at that position. Next, in a state in which a compressive force is applied to the metal tube 1 via the movable support 3 with a compression device (not shown), a small region in the longitudinal direction of the metal tube 1 is heated by the heating device 4 to cause plastic deformation. The heating unit 5 is in an easily red hot state, and the heating unit 4 is moved in the direction of the arrow C along the metal tube 1 while causing the heating unit 5 to increase in thickness due to compressive force. 7 is sprayed on the rear end portion of the heating unit 5 to cool and solidify the portion immediately after the thickening. Thereby, the metal pipe 1 is continuously increased in thickness in the longitudinal direction, and the thick portion 1A is formed. Then, when the thick part 1A having the desired length L is formed, the above-described operation is finished.
[0019]
If the die 10 is not used during the above thickening process, unstable deformation (for example, deformation in which a flat side wall is recessed or a bellows shape in the longitudinal direction) may occur in the thickened portion. Since the outer surface of the die 10 is located inside the thickened portion of the metal tube 1, such unstable deformation can be prevented and a good thickness increasing process can be performed.
[0020]
As shown in FIG. 3, after the thick portion 1 </ b> A having a predetermined length is formed on the outside of the die 10, the thick portion 1 </ b> A is heat-treated while the die 10 is placed in that position as necessary. This heat treatment is performed on the entire length of the thick portion 1A by locally heating the thick portion 1A with the heating device 4 (see FIG. 1) and moving the heating device 4 along the thick portion 1A. it can. Alternatively, as described in JP-A-9-76011, an auxiliary heating device for heat treatment can be provided behind the heating device 4 to perform heat treatment in parallel with the thickening operation. Also during such heat treatment, since the die 10 is inside the thick portion 1A and the inner surface of the thick portion 1A is restricted, undesirable thermal deformation can be prevented.
[0021]
After completion of the thickening process or after the heat treatment, a drawing force is applied to the die 10 by a die moving device (not shown), and the die 10 is drawn from the metal tube 1. When the die 10 is pulled out, the inner surface of the thick portion 1A is pressed against the outer surface of the die 10, and pulling resistance due to friction acts. As shown in FIG. 3, the pressing force (clamping force) of the thick portion 1A against the outer surface of the die 10 is Q, the inclination angle of the outer surface of the die 10 is θ, and the friction coefficient between the thick portion 1A and the die 10 is μ. If the maximum friction angle is ρ and the force required to pull out the die 10 (pulling force) is F, this force F is expressed by the following equation.
F = Q tan (ρ−θ) (1)
Here, ρ = tan ⁻¹ μ (2)
[0022]
Therefore, the die 10 moves in the axial direction with respect to the metal tube 1 by applying the force F satisfying the expression (1) to the die 10. When the die 10 is slightly moved with respect to the metal tube 1, a gap is formed between the inner surface of the thick portion 1 </ b> A and the outer surface of the die 10 due to the gradient provided on the outer surface of the die 10. The pressing force Q decreases rapidly. For this reason, the pulling force F also decreases rapidly, and the die 10 can be pulled out very lightly. Further, since the die 10 is not pulled out while the thick portion 1A is strongly pressed against the die 10, the inner surface of the thick portion 1A is not damaged when the die 10 is pulled out. Thus, in this embodiment, even if a certain amount of pulling force is required at the start of pulling out the die 10, the die 10 can be pulled out with a very light force after the die 10 has moved even slightly, and the die 10 can be pulled out. It can be pulled out easily and without scratching the inner surface of the metal tube. In order to give a large pulling force to the die 10 at the start of pulling out the die 10, the support shaft 12 may be hit in the axial direction by an appropriate hitting means and the die 10 may be moved a little. If comprised in this way, it will become unnecessary to generate | occur | produce a too big force in the dice movement apparatus for taking in / out the dice | dies 10, and it can achieve size reduction of an apparatus.
[0023]
The thickening process described above is usually performed so that the thickness increase rate is constant, that is, the thickness of the thick portion is uniform. Therefore, as shown in FIG. 3, the thick portion 1 </ b> A formed by the thickening has an outer surface 1 </ b> Aa that is parallel to the outer surface 10 a of the die 10, and is inclined with respect to the axis OO of the metal tube 1. It becomes the shape. However, since the gradient formed in the die 10 is extremely small, the difference in outer diameter between the large diameter side and the small diameter side of the thick portion 1A does not matter so much. For example, when a thick portion of 500 mm is formed with a gradient of 1/500, the outer diameter difference between the large diameter side and the small diameter side is about 2 mm, compared to the outer diameter of the metal tube 1 (usually about 200 mm or more). 1% or less, often acceptable.
[0024]
However, some products require the outer diameter to be strictly uniform. When dimensional tolerances are strictly required in this way, the thickness increase rate of the thick wall portion is increased according to the longitudinal position of the metal tube 1 and the gradient of the die 10 to increase the thickness. As shown in FIG. 4, the thickness of the thick portion 1B is changed according to the gradient of the die 10 so that the outer surface 1Ba of the thick portion 1B is parallel to the axis OO of the metal tube 1, and thus the outer diameter dimension. Can be made equal along the length of the metal tube. Here, if the thickness increase rate β is defined as “thickness increased by thickness increase / thickness before thickness increase”, the thickness increase rate β is determined by the moving speed of the heating unit 5 in FIG. With respect to the moving speed W of the heating device 4 and the moving speed of the unthinned portion of the metal tube 1 pushed toward the heating unit 5, that is, the moving speed V of the movable support 3.
β = V / W (3)
The relationship is shown in. Therefore, by adjusting (changing) one or both of the moving speed W of the heating device 4 and the moving speed V of the movable support 3 in accordance with the position in the longitudinal direction of the metal tube 1, the thickness increase rate β is increased. It can be changed as desired along the longitudinal direction of the tube 1, and the outer diameter of the thick portion 1A formed outside the die 10 having a gradient can be made constant in the longitudinal direction.
[0025]
In adjusting the thickness increase rate β, the method of adjusting the moving speed V of the movable support 3 is as follows: 1) The temperature of the heating unit 5 is kept constant (therefore, the deformation resistance of the heating unit is kept constant). ) To change the pressing force of the compression device (not shown) applied to the movable support 3, and 2) heating in a state where the pressing force of the compression device (not shown) applied to the movable support 3 is kept constant. 3) Method of changing the temperature of the part 5 3) As a compression device for moving the movable support 3, the speed at which the movable support 3 is moved can be controlled (for example, equipped with a digital cylinder, a digital servo mechanism, etc.) And the like.
[0026]
In the above embodiment, as can be seen from FIG. 2, a square tube having an outer surface similar to the inner surface of the metal tube 1 is used as the die 10, but the die used in the present invention is not necessarily connected over the entire circumference. It is good also as what is comprised not only in a tubular thing but in a plurality of segments. For example, a die 10A composed of four segments 10Aa shown in FIG. 5A or a die 10B composed of four segments 10Ba shown in FIG. 5B can be used. When using the dice 10A or 10B composed of these multiple segments 10Aa or 10Ba, there will be a gap between the segments, but these segments do not need to be expanded or contracted with respect to the center, The gap can be made extremely small, and there is no problem in supporting the inner surface of the thick portion during the thickening process.
[0027]
Furthermore, in the embodiment shown in FIG. 1, the die 10 is configured to be taken in and out of the metal tube 1 from the movable support 3 side. May be. In that case, of course, the gradient formed in the die 10 is such that the end on the fixed support 2 side is on the large diameter side.
[0028]
FIG. 6 is a schematic cross-sectional view showing an example different from FIG. 1 of the thickening apparatus used for carrying out the method of the present invention, and FIGS. 7A and 7B are a thick-walled part during and at the end of thickening process, FIG. 6 is a schematic cross-sectional view showing a die, and parts that are the same as or similar to the apparatus shown in FIGS. 6 and 7, the die 20 inserted into the metal tube 1 is short enough to support the inner surface of a short region including the heating part 5 of the metal tube 1. A die moving device (not shown) connected to the support shaft 22 supporting the die 20 and moving the die 20 in the axial direction of the metal tube 1 is provided on the side where the die 20 is withdrawn from the metal tube 1. A function of moving in synchronization with the heating device 4 is provided. On the outer surface of the die 20, a gradient is formed along the longitudinal direction of the metal tube 1 over its entire length so that the side from which the die 20 is drawn from the metal tube 1 (the left side in FIG. 1) has a large diameter. ing. The gradient is preferably larger than the gradient of the die 10 in the apparatus shown in FIG. 1, for example, about 1/10 to 1/2 (inclination angle θ is 5.7 ° to 26.6 °). Set to. Other configurations are the same as those of the apparatus shown in FIG.
[0029]
In this apparatus, the die 20 moves to the drawing side from the metal tube in synchronism with the movement of the heating device 4 at the time of the thickening process, and as a result, as shown in FIG. The die 20 is always located inside the portion where it is located and regulates its inner surface. Thereby, unstable deformation at the time of thickening is prevented. Then, as shown in FIG. 7B, at the time when the thickening operation is finished, the die 20 is only located at the end of the thick portion 1C, and a gradient is formed in the die 20. Therefore, the die 20 can be pulled out very easily. Furthermore, since the inclination angle θ is set to be large, as can be seen from the above equation (1), the pulling force F becomes small, the force for moving the die 20 during the thickening process, and the die 20 after the thickening is finished. Any force required for pulling out can be reduced. Moreover, in this embodiment, the outer surface of the thick portion 1C can be made parallel to the axis of the metal tube by keeping the thickness increase rate constant.
[0030]
【The invention's effect】
As described above, the present invention uses a die having a gradient along the longitudinal direction of the metal tube as the die to be inserted into the metal tube, thereby reducing the diameter when the die is pulled, Without performing operations such as disassembling, the die can be easily pulled out without damaging the inner surface of the metal tube. Therefore, an inexpensive die with a simple structure that does not include an expansion / contraction mechanism or a disassembling mechanism can be obtained. It can be used, and the cost of the apparatus used for bending can be reduced, the die maintenance is simplified, and the maintenance cost can be reduced.
[0031]
Here, if a die having a length that can support the entire length of the thick portion formed by thickening is used, the thick portion can be formed on the outer surface of the die stopped at a fixed position. Heat treatment can be performed in a state where the thick portion is supported, and an effect that heat treatment can be performed without causing unstable thermal deformation in the thick portion is obtained.
[0032]
In addition, if a short die that moves in synchronism with the heating part formed on the metal tube for thickening is used, the die can be shortened, so that the cost of the die can be further reduced and the drawing can be performed more easily. The effect that it can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a preferred example of a thickening apparatus used for carrying out the method of the present invention. FIGS. B is a cross-sectional view taken along the arrow B. FIG. 3 is a schematic cross-sectional view showing a thick portion and a die at the end of the thickening process in the apparatus shown in FIG. 1. FIG. [Fig. 5] (a) and (b) are schematic end views showing modified examples of the dies. [Fig. 6] Fig. 6 shows another example of a thickening apparatus used for carrying out the method of the present invention. Schematic sectional view [Fig. 7] (a) and (b) are schematic sectional views showing thick portions and dies in the middle and at the end of the thickening process in the apparatus of Fig. 6, respectively.
DESCRIPTION OF SYMBOLS 1 Metal pipe 1A, 1B, 1C Thick part 2 Fixed support body 3 Movable support body 4 Heating device 5 Heating part 6 Cooling device 7 Cooling medium 8 Moving device 10, 10A, 10B Dice 10Aa, 10Ba Segment 11 Support material 12 Support shaft 20 Dice 22 Support shaft

Claims (4)

In this state, a die having a length equal to or greater than the length of the thick wall portion is inserted in advance in the metal tube to be thickened so as to be positioned inside the thick wall portion formed by the thickening processing. Then, a small region in the longitudinal direction of the metal tube is locally heated by a heating device to form a red-hot state heating portion, and while the heating portion is moved in the longitudinal direction of the metal tube, In order to increase the thickness sequentially by applying a compressive force in the direction, and to cool the rear end portion of the heating unit immediately after the thickness increase, the metal tube is continuously increased in thickness, and the thick portion is formed outside the die. In the forming method, as the die, a metal tube thickening process characterized by using a die having a gradient with a large diameter on the drawing side from the metal tube along the longitudinal direction of the metal tube on the outer surface thereof Method.   While adjusting the thickness increase rate of the thick portion according to the longitudinal position of the metal tube and the gradient of the die so that the outer diameter dimension of the thick portion becomes equal along the longitudinal direction of the metal tube 2. A method for increasing the thickness of a metal pipe according to claim 1, wherein the thickness is increased.   The method for increasing the thickness of a metal tube according to claim 1 or 2, wherein a gradient of the die is set to 1/1000 to 1/100. A small area in the longitudinal direction of the metal tube to be thickened is locally heated with a heating device to form a red-hot state heating section, and the heating section is moved in the longitudinal direction of the metal pipe while moving the metal to the heating section. By applying a compressive force in the longitudinal direction of the tube to gradually increase the thickness, and cooling the rear end portion of the heating portion immediately after the thickness increase, the metal tube is continuously increased in thickness to form a thick portion. In the method, a die whose outer surface is provided with a gradient along the longitudinal direction of the metal tube so as to be located inside the heating unit of the metal tube, the large-diameter side of the gradient is a drawing side, and the metal tube of the heating unit is provided. position is allowed Rutotomoni thickening processing method of the metal tube, characterized in that for relatively moving the die to the metal tube tuned to move with respect to the metal tube of the heating unit such that the moving direction side with respect to.

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